1. Field of the Invention
This invention relates to sacrificial anodes and protective coatings and their use especially in underground installations.
2. Description of the Prior Art
In laying underground pipe, the pipe sections are welded end-to-end, the cutback, i.e. the area at the joint where the mill-wrap coating is removed, is coated and the assembled pipe is then dragged to location and plowed in to location or lowered in a trench and back-filled. Although many forms of sacrificial anodes are described in the patent art, present commercial methods for cathodic protection of coated pipes to be installed underground, e.g., gas lines, water lines, and the like, involve placing the anode in an adjacent underground location and running an underground lead wire from the anode to the pipe. The lead wire is then welded to the pipe which disrupts the coating. The pipe must then be recoated at the weld site which is an expensive and time consuming operation. Anodes are usually installed at intervals of about 1000 feet along the pipe and the anodes are of sufficient size and spaced a sufficient distance from the pipe for protecting the length of pipe therebetween.
More particularly, the installation of such anodes involves digging a separate trench for each anode extending outward from the main trench which receives the pipe. The pipe is placed in the main trench and an anode is placed at the end of each separate anode trench; the lead wires are extended back to the pipe and brazed or welded to the pipe. The welding sites are recoated and the anode installation trenches and pipe trenches are filled to complete the installation.
Such operation sometimes results in incomplete electrical contact of the lead wire to the pipe because of the presence of primers or coating materials at the weld site. At times a worker in the field will either forget or neglect to attach the anode or will simply omit the anode because of the additional work involved for the anode installation. Other disadvantages of this type of installation arise from failure or error in recording anode locations for future reexcavation, damage to lead wires by other and later excavation, failure to install the anode at a proper depth and excessive cost of this method of anode installation. Also, the anodes now conventionally used cannot be attached to the pipe and plowed or dragged with the pipe to the installation site because they will snag during plowing or dragging and become disconnected from the pipe.